Medical respirator

ABSTRACT

A liquid injector for medical respirators in which a predetermined quantity of patient gas is stored at higher than atmospheric pressure in a known volume during an expiratory period of a respiratory cycle and discharged to a patient during the next following inspiratory period of the cycle. The injector includes a movable member the displacement of which from a datum position controls the quantity of liquid injected into the patient gas in each cycle. This displacement is directly proportional to the pressure of the stored patient gas and the movable member is displaced by driving means which is driven as a result of the pressure.

United States Patent 1 Kipling [54] MEDICAL RESPIRATOR [75] Inventor:Barry John Kipling, Cambridge, En-

gland [73] Assignee: U.S. Philips York,N.Y.

[22] Filed: Feb. 8, 1971 [21] Appl. No.: 113,279

Corporation, New

[30] Foreign Application Priority Data 9/1970 Schreiber ..128/188 1 May22, 1973 3,523,527 8/1970 Foster "128/1456 3,530,873 9/1970 Arp..128/l45.6X

[57] ABSTRACT A liquid injector for medical respirators in which apredetermined quantity of patient gas is stored at higher thanatmospheric pressure in a known volume during an expiratory period of arespiratory cycle and discharged to a patient during the next followinginspiratory period of the cycle. The injector includes a movable memberthe displacement of which from a datum position controls the quantity ofliquid injected into the patient gas in each cycle. This displacement isdirectly proportional to the pressure of the stored patient gas and themovable member is displaced by driving means which is driven as a resultof the pressure.

10 Claims, 3 Drawing Figures VZM/ ll PATENTEWYZZIW 3,734,092

SHEET 1 OF 3 PR A Mi f FC F ig.1

INVEN'IOR.

BARRY JOHN KI PLING PATENTEL H312 2 i975 INVENTOR.

BARRY JOHN KIPLING AGEN Fig.3

MEDICAL RESPIRATOR This invention relates to liquid injectors formedical respirators in which a predetermined quantity of patient gas isstored at higher than atmospheric pressure in a known volume during anexpiratory period of a respiratory cycle and discharged to a patientduring the next following inspiratory period of the cycle. Inrespirators of the type described, sometimes referred to as tidalvolume" respirators, the quantity of gas passed to a patient perrespiratory cycle, i.e. the tidal volume, is proportional to the productof the gas pressure and the known volume. This quantity may therefore bevaried by controlling the pressure of the patient gas fed to andstoredin the known volume.

In medical respirators, it is sometimes required that a quantity ofliquid be added to the patient gas in each respiratory cyele; this beingeffected by a liquid injector. The quantity of liquid normally used percycle is very small in relation to the tidal volume and must beaccurately controlled. The quantity per cycle is usually expressed as aratio of liquid, or liquid vapor, to patient gas.

An object of the invention is the provision of a liquid injector forrespirators of the type described in which alteration of the patient gaspressure to adjust the tidal volume also affects the quantity of liquidinjected by the injector such that the liquid/gas ratio of the mixturedischarged to the patient is held constant.

According to one aspect of the invention, the injector includes amovable member the displacement of which from a datum position controlsthe quantity of liquid injected into the patient gas in each cycle; thesaid displacement being directly proportional to the pressure of thestored patient gas.

According to a further aspect of the present invention, spring means areprovided which control the displacementof the movable member by exertinga force tending to oppose the displacement.

According to a further aspect of the invention there is provided aliquid injector, for a medical respirator of the typedescribed, in whichpatient gas at the said pressure is appliedduring the expiratory orinspiratory period to displace a movable member to transfer liquid froma reservoir to the predetermined quantity of patient gas, and in whichspring means control thedisplacement of the movable member to hold theliquid/- gas ratio in the mixture of liquid and gas fed to the patientconstant with change of the said pressure.

The above and other features of the invention will be more readilyunderstood by a perusal of the following deseriptioh' of exemplaryembodiments thereof having reference to the accompanying drawings inwhich:

FIG. 2 shows one embodiment of the invention in which the injector anddrive system operate in the inspiratory period of a Tidal VolumeRespirator;

FIG. 3 shows an alternative to FIG. 2 in which liquid is delivered tostored patient gas during an expiratory period","tliemixture of liquidand gas being delivered in the next following inspiratory period.

In FIG. 1 a'p'ressure driven motor M, which may be a cylinder enclosinga piston or bellows, giving linear movement with applied pressure, iscoupled by a mechanicallink ML to aninjector I of a type in whichdisplacement of liquid is proportional to displacement of a movablemember. An extension E of link ML is engaged with one end of a springSP, whose other end is fixed. The motor input is connected by a line 11to a switch SW, which, in the shown position, connects the input of themotor M to atmosphere as indicated by an arrowhead A. In the shownposition spring SP is unstressed. A liquid reservoir LR suppliesinjector I via a line 12 and a one way valve D1, and liquid frominjector I is passed to atmosphere, arrowhead A, via a second one wayvalve D2 and line 13.

Movement of switch SW to its alternative position connects gas atadjustable pressure in line 15, supplied from pressure regulator PR fedvia line 14 from a source PS of gas at higher than atmospheric pressure,to the motor input, and motor M will be driven. Such drive will movelink ML and the movable member of the injector by an amount depending onthe gas pressure and the opposed force from the now compressed springSP. Adjustment of gas pressure may therefore control the amount ofliquid displaced from injector I.

Substitution of a spring of different rate, i.e. one in which thedeflection for a given applied force is not the same as that for springSP, will, at any gas pressure applied to motor M, result in a differentliquid displacement per unit of gas pressure. For a fixed pressure,therefore, a means controlling the spring rate may be calibrated interms of liquid delivered on each operation of switch SW.

As described above, a quantity of liquid will be delivered from injectorI immediately after switch SW connects the motor M to gas pressure. Thedelivery may be prolonged by the inclusion of resistance to flow, as forexample, by a flow control FC in line 13 from the outlet of the injectorI.

In FIG. 2, the scale of which is not uniform, a pneumatically operatedspool valve 60 is controlled by air pressure supplied by air linesconnected to control ports 29 and 66, the arrangement being such that apneumatic timing circuit supplies pressure to port 29, with port 66vented to atmosphere, during an inspiration period, and suppliespressure to port 66, with port 29 vented, during an expiration period. Acylinder 50 contains a piston 54, having unequal area end faces 52 and51 (the area of latter being greater than the former) which divides thecylinder into two volumes V1 and V2. During an expiratory period, withthe spool or shuttle of valve 60 in its alternative position to thatshown so that a passage is established between valve ports 47 and 48,gas in volume V2 is transferred to volume V1 via pipe lines 53, 46 and49. Additional gas is provided from a pressure source (not shown)connected to port 43 at a pressure determined by a regulator 45connected between ports 47 and 43 by pipe lines 46 and 44. During thisexpiratory period piston 54 moves towards the left to increase: thecapacity of volume V1 and the quantity of gas stored in volume V1, thetidal volume, is the product of pressure as determined by regulator 45and the maximum capacity of volume V1 when in its extreme left handposition.

During an inspiratory period, valve 60 establishes a passage as shownbetween ports 48 and 55, and gas passes from volume V1 via pipe lines 49and 56 to a flow control 57 and thence to a patient via line 58. Duringthis period pressure in pipe line 56 is substantially constant due tothe movement of piston 54 to the right under the influence of gaspressure from regulator 45 applied to volume V2 via pipe lines 46 and53.

For injection of liquid during an inspiratory period the pressure inpipe line 56 is utilized by applying it to a piston 20, within acylinder 20A, via a pipe line 21; the resulting movement of piston 20under the influence of the pressure being transferred by a piston rod20B to a plunger 22, working within a cylinder 22A, which togethercomprise an injector. Piston 20 is preferably of larger diameter thanplunger 22 and of much smaller diameter than piston 54. A recessedcollar 20C is secured to piston rod 20B and engages one end of a springblade 23 attached to an anchoring bar 23A. The position of another bar23B, slidable on bar 23A, determines the point at which flexure ofspring blade 23 may commence, the arrangement of bars 23A, 23B andcollar 20C being such that, with no pressure in cylinder 20A, the springblade 23 is substantially unstressed and the volume defined by piston 20and cylinder 20A is substantially zero.

Fluid, from a reservoir not shown, is supplied to the injector cylinder22A via a fluid line 24 and a one way valve D1 and may leave theinjector by way of fluid line 25 having a one way valve D2 therein.Valve D2 is very lightly spring loaded so that the head of fluid withinthe reservoir and injector does not of itself cause liquid to flowbeyond it. A liquid flow control 26 receives liquid from line 25 andpasses it to a patient via a line 27 joined to the patient gas line 58.

Movement of bar 23B relative to bar 23A may be by any conventionalcontrol means, and, as such movement alters the spring rate andtherefore the deflection for a given applied force, the control may becalibrated in terms of liquid ejected. Alteration of pressure, byregulator 45, not only alters the deflection and amount of liquidejected for a given position of bar 238, but also the quantity of gasstored per expiratory period; the tidal volume of gas being delivered toa patient in the next following inspiratory period. The control formovement of bar 23 may therefore be calibrated in terms of the ratio ofliquid to patient gas per respiration or, for a given temperature andwith a volatile liquid, in terms of the ratio or percentage of liquidvapor to patient gas, such ratios remaining constant during changes oftidal volume caused by alteration of gas pressure.

Certain small disadvantages are apparent in such a system:

a. The volume of gas in cylinder 20A discharges substantiallyexponentially to the patient through flow control 57 after piston 54 hasreached its extreme right hand position and/or valve 60 has operated toterminate an inspiratory period. This advantage may be made negligibleby arranging that the maximum volume within cylinder 20A and piston 20is small and also small relative to the maximum capacity of volume V1.As the maximum quantity of liquid to be injected is small, this isreadily achieved.

b. Liquid flow control 26 must be adjusted, in addition to the pneumatictiming controls and gas flow control 57 of the respirator, so thattransfer of liquid from the injector to line 58 and the patient occurswithin the set inspiratory period.

c. Deflection, and therefore liquid ejected, is proportional to the cubeof the effective length of spring blade 23, making difficult theprovision of a linear scale for the control means.

The above disadvantages are overcome, either completely or partially, inthe injection system shown in FIG. 3 in which gas within a storagevolume is injected with liquid during an expiratory period, the mixtureof gas and liquid being passed to the patient in the next followinginspiratory period.

In FIG. 3, in which the scale employed is not uniform, walls 74, 75 and76 contain two rigid diaphragms and 72, connected by a spacing member 79fixed thereto and having respective flexible surrounds 71 and 73, todefine two volumes V1 and V2 with respective entry ports 83, 83A and 82.

Parts concerned with liquid injection are a bellows 30, sealed in acontainer 30A to define a volume V3, which drives a plunger 32 within acylinder 32A by means of a linking piston rod 308 when gas pressure isintroduced into volume V3 by a pipe line 31C; plunger 32 and cylinder32A forming at least part of an injector.

Liquid for the injector is supplied from a reservoir, not shown, vialiquid pipe line 34 containing a one way valve D1, and leaves theinjector by line 35 containing a second one way valve D2 which islightly spring biased to the closed position.

A spring 33 has one end attached to an anchoring member 33A whichcarries, in slidable engagement, a fulcrum member 33B. Pivoted onfulcrum 33B is a bar 33C to one end of which is attached the other endof spring 33. The other end of bar 33C is bifurcated to embrace pistonrod 308, a pin 30C therein engaging the upper surface of bar 33C. Twopairs of rods 33D, mounted on anchorage 33A, act as guides for bar 33Cduring movement. Guides, not shown, on bar 33C prevent horizontalmovement of the bar relative to pin 30C.

In this expiratory period injection system it is essential that thepressurized area of bellows 30, corresponding to the area of piston 20in FIG. 2, is greater than the working area of plunger 32.

Patient gas at pressure is applied to a port 36 of the tidal volumerespirator and is passed on line 37 to a pressure regulator 38 fromwhence it issues on a line 31 to port 82 of volume V2. Branches 31A and31B of line 31 respectively feed ports A of two spool valves 39 and 40.Valves 39 and 40 work in unison and may be'driven either mechanically orby other means. Their operation from the shown beginning of aninspiratory period terminates such period and starts an expiratoryperiod which, in turn, is terminated by reverting the valves to theshown position. The drive and timing means for these valves are notshown.

During an inspiratory period gas pressure applied to port 82 expandsvolume V2 and drives the contents of volume V1 out of port 83A, via aline 41, ports B and C of valve 40, a line 56, a flow control 57 and aline 58, to a patient connected thereto. During this period volume V3 isreduced to a minimum, which may be substantially zero, due to thepassage within valve 39 to atmosphere, indicated by an arrowhead issuingfrom port C, established from port B to which line 31C is connected.With a minimum volume V3 established the arrangement is such thatneither bellows 30, which may be of metal, or spring 33, are stressedbut pin 30C is in contact with bar 33C.

On change over of valves 39 and 40 to their expiratory position,communication to the patient is closed at port C of valve 40 and gas atpressure is passed to volume V1 via ports A and B of that valve, drivingthe diaphragm assembly towards the position shown. At the same time apath is established in valve 39 between ports A and B, applying pressureto volume V3, so contracting bellows 30 and moving plunger 32. Theamount of such movement and of liquid ejected thereby is governed byforces acting in opposition to the pressure in volume V3 which comprisethe tension in the now elongated spring 33 multiplied by any mechanicaladvantage given by the position of fulcrum 338 plus pressure from volumeV1 acting on plunger 32 and any force exerted by compressed bellows 30.

Pressure in volume V1 may be regarded as substantially constant at thepressure set by regulator 38, which pressure is also applied to volumeV3, so that movement of plunger 32 is proportional to the pressuredetermining tidal volume for any position of fulcrum 338, which maytherefore be calibrated, as for FIG. 2, in terms of the ratio of liquidto patient gas.

Movement of fulcrum 33B may be controlled, as for FIG. 2, by knownmeans, e.g. threaded rod and nut, rack-and-pinion gears or cam andspring. As the opposing force exerted by the spring 33 is proportionalto Ds/Dp, where Ds is the distance between spring and fulcrum and Dp isthe distance between fulcrum and pin 30C, the movement calibration offulcrum 33B departs from linearity less than in the case of thecantilever spring blade of FIG. 2. Where cam movement means are employedto linearize the scale a less steep profile is required.

In FIGS. 2 and 3 a simple type of plunger operated injector is shown. Itmay be replaced in both figures by a more complex type as described andshown in FIG.

3 of copending US. application Ser. No. 6,846 in which piston 72corresponds to plunger 22 or 32. In FIG. 3 of the present application abroken line 31D represents a source of driving pressure for the cylinder66 of FIG. 3 of US. application 6,846, broken line rectangles shown inboth lines 31C and 31D indicating means e.g. restrictions and/or one wayvalves to control the required sequential action of the two moving partsof the more complex injector. With such an injector, one way valve D1becomes superfluous and one way valve D2 is incorporated in theinjector.

Gas from volume V3 discharged to atmosphere from port C of spool valve39 represents wastage which may be small due to the small maximumcapacity of volume V3. Such wastage may be eliminated by connecting portC of valve 39 to line 58 and so to the patient.

Other forms of construction of the various parts of the injection systemof FIG. 3 are possible. The bellows 30 and container 30A may be replacedby the piston and cylinder of FIG. 2, as may be the tension springarrangement by the equivalent cantilever or quarter elliptic springsystem. Where a simple type of injector such as shown in FIGS. 2 and 3is employed, cylinder 32A may be within a wall of volume V1, e.g. wall75 in FIG. 3.

Other modifications are also possible. For example, in FIG. 2, to avoidusing the liquid flow control 26, liquid pipe line 25 may be takeninstead to gas pipe line 56 downstream of the junction with line 21. Insuch case piston 20 must be of greater diameter than plunger 22 andpreferably a third one way valve is inserted in line 56 between thejunctions of lines 21 and 25 to prevent liquid passing into line 21.Spring blade 23 also may have nonuniform dimensions throughout itslength or be comprised of more than one blade to assist in obtaining alinear scale to the control for movement of bar 23B.

What we claim is:-

1. In a medical respirator comprising a cylinder for containing patientgas at a storage pressure which is higher than atmospheric pressure, apiston having opposite end faces thereof of unequal areas movable withinsaid cylinder and dividing said cylinder into first and second volumes,first connection means connected to a source of gas and to said firstvolume for supplying patient gas thereto during an expiratory period ofsaid respirator, second connection means connected to said first volumefor passing patient gas therefrom to a patient during an inspirationperiod of the respirator, switching means for connecting said firstvolume to said first or second connection means during expiration orinspiration periods, means connected to said switching means forcyclically operating said switch, means connected to said second volumefor supplying gas thereto the pressure of which acts on said piston toexpel the gas within said first volume, a liquid injector means forinjecting an adjustably predetermined quantity of liquid into thepatient gas to be passed to the patient comprising a variable volumecontainer for the liquid, driving means connected to said variablevolume liquid container and operable by said storage pressure of saidgas to reduce the volume of said liquid container to cause liquid to bedischarged therefrom into the said quantity of gas, means connectingsaid driving means to said switch for applying said gas at storagepressure to said driving means to cause operation thereof so that thequantity of liquid discharged is proportional to the said storagepressure of the gas, and a spring control means for adjustalblycontrolling said driving means having increasing restitution force withincreasing deflection from an unstressed position acting on the drivingmeans in such a direction as to tend to oppose movement thereof, causedby the gas for reducing the volume of said liquid.

2. In the medical respirator according to claim 1 wherein the variablevolume container comprises a piston in a cylinder.

3. In the medical respirator according to claim 2 wherein the drivingmeans is a piston in the cylinder.

4. In the medical respirator according to claim 1 wherein the drivingmeans is a bellows.

5. In the medical respirator according to claim 1 wherein the spring isa helical spring.

6. In the medical respirator according to claim 1 wherein the spring isa blade spring.

7. In the medical respirator according to claim 1 further comprisingmeans for adjusting the increase of restitution force of the spring withincrease of deflection.

8. In a medical respirator according to claim 1 further comprising flowrate controlling means connected to said liquid container forcontrolling the rate at which liquid is passed from the container intothe said quantity of gas.

' 9. In the medical respirator according to claim 1 further comprisingmeans connected to said liquid container'for delivering the quantity ofliquid which is discharged therefrom into the stored quantity of gaswithin said first volume during an expiratory period.

10. In the medical respirator according to claim 1 further comprisingmeans connected to said liquid container for delivering said quantity ofliquid which is discharged therefrom into the predetermined quantity ofgas while the gas is being passed to the patient during an inspiratoryperiod.

=8 III I it 52 3 3 UNITED STATES PATENT @FFME QERTIFICATE OF CQRREQTWNPatent No. 3734-092 Dated May 22, 1973 Inventor(s) BARRY JOHN KIPLING Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In the heading, "Assignee" should read ----PYE LIMITED-- Signed andsealed this 19th day of February 1974.

(SEAL) Attest;

EDWARD M.FLETCHER,JR. C. MARSHALL N Attestlng offl Commissioner ofPatents

1. In a medical respirator comprising a cylinder for containing patientgas at a storage pressure which is higher than atmospheric pressure, apiston having opposite end faces thereof of unequal areas movable withinsaid cylinder and dividing said cylinder into first and second volumes,first connection means connected to a source of gas and to said firstvolume for supplying patient gas thereto during an expiratory period ofsaid respirator, second connection means connected to said first volumefor passing patient gas therefrom to a patient during an inspirationperiod of the respirator, switching means for connecting said firstvolume to said first or second connection means during expiration orinspiration periods, means connected to said switching means forcyclically operating said switch, means connected to said second volumefor supplying gas thereto the pressure of which acts on said piston toexpel the gas within said first volume, a liquid injector means forinjecting an adjustably predetermined quantity of liquid into thepatient gas to be passed to the patient comprising a variable volumecontainer for the liquid, driving means connected to said variablevolume liquid container and operable by said storage pressure of saidgas to reduce the volume of said liquid container to cause liquid to bedischarged therefrom into the said quantity of gas, means connectingsaid driving meanS to said switch for applying said gas at storagepressure to said driving means to cause operation thereof so that thequantity of liquid discharged is proportional to the said storagepressure of the gas, and a spring control means for adjustablycontrolling said driving means having increasing restitution force withincreasing deflection from an unstressed position acting on the drivingmeans in such a direction as to tend to oppose movement thereof, causedby the gas for reducing the volume of said liquid.
 2. In the medicalrespirator according to claim 1 wherein the variable volume containercomprises a piston in a cylinder.
 3. In the medical respirator accordingto claim 2 wherein the driving means is a piston in the cylinder.
 4. Inthe medical respirator according to claim 1 wherein the driving means isa bellows.
 5. In the medical respirator according to claim 1 wherein thespring is a helical spring.
 6. In the medical respirator according toclaim 1 wherein the spring is a blade spring.
 7. In the medicalrespirator according to claim 1 further comprising means for adjustingthe increase of restitution force of the spring with increase ofdeflection.
 8. In a medical respirator according to claim 1 furthercomprising flow rate controlling means connected to said liquidcontainer for controlling the rate at which liquid is passed from thecontainer into the said quantity of gas.
 9. In the medical respiratoraccording to claim 1 further comprising means connected to said liquidcontainer for delivering the quantity of liquid which is dischargedtherefrom into the stored quantity of gas within said first volumeduring an expiratory period.
 10. In the medical respirator according toclaim 1 further comprising means connected to said liquid container fordelivering said quantity of liquid which is discharged therefrom intothe predetermined quantity of gas while the gas is being passed to thepatient during an inspiratory period.